Postgraduate Medicine

ISSN: 0032-5481 (Print) 1941-9260 (Online) Journal homepage: http://www.tandfonline.com/loi/ipgm20

Health benefits of aerobic exercise David J. Mersy MD To cite this article: David J. Mersy MD (1991) Health benefits of aerobic exercise, Postgraduate Medicine, 90:1, 103-112, DOI: 10.1080/00325481.1991.11700983 To link to this article: http://dx.doi.org/10.1080/00325481.1991.11700983

Published online: 17 May 2016.

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-@CME credit article

Health benefits of aerobic exercise

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David J. Mersy, MD

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rate. Improvement in Vo2 max can

Aerobic exercise can play a role in the management and prevention of many of the conditions primary care physicians encounter on a daily basis-coronary artery disease, obesity, depression, and diabetes, to name a few. Dr Mersy reviews what every physician needs to know about the contributions of exercise to health.

be maintained by exercising only

Aerobic exercise is a topic of continuing interest to patients and physicians. More and more people are initiating endurance-training activities, a trend that started in the 1960s. In order to advise patients, primary care physicians need to be aware of the many health benefits of embarking on a program of aerobic exercise. They also need to recognize potential problems of exercising and know how to deal with them.

Prescribing a program of exercise Aerobic exercise is usually defined as exercise that is maintained by using oxygen delivered by the blood to the exercising muscles. Aerobic metabolism of this son occurs during exercise oflow intensity and long duration.' Exercise ofhigh intensity and shan duration is anaerobic-that is, it uses oxygen already present in the muscle, because the exercise is of such intensity that the blood supply cannot keep up with the muscle's demand for oxygen. To qualifY as aerobic, exercise must involve large muscle groups, be steady, and last long enough to produce a training effect. Running, fast walking, bicycling, swimming, skating, cross-country skiing, and aerobic dancing are some

endurance activities that meet these criteria. To develop and maintain cardiorespiratory fimess and body composition, healthy adults need 15 to 60 minutes of continuous aerobic exercise 3 to 5 days per week at 60% to 90% of maximum hean rate, according to the American College of Sports Medicine (table 1). 2 A practical way to determine a person's maximum hean rate is to subtract his or her age &om 220. Thus a 40-year-old person's maximum hean rate would be 180 (220- 40); that person's target hean rate would then be 108 to 162 beats per minute (60% to 90% of the maximum). The 60% level should be used to calculate the target rate for markedly deconditioned persons just beginning an exercise program, whereas the target rate for the average healthy adult should be in the range of70o/o to 85% of the maximum. In order to assure improvement in work capacity (as measured by incr?Se in maximum oxygen uptake [Vo 2max]), exercise must be performed three to five times per week for at least 20 minutes per session at 70% or more of maximum hean

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twice a week. Discontinuation of exercise rest_llts in loss of most improvement in Vo2max within 5 weeks. 3 Significant reductions in fimess have been found as early as 2 weeks after training was stopped. 4 Thus, once patients begin a program of aerobic exercise, it is imponant to keep them motivated to sustain it. People are more likely to continue exercising if they choose an activity they enjoy. Brisk walking is an excellent form of exercise that many people will continue doing.

Cardiovascular benefits The many beneficial physiologic responses to aerobic exercise (table 2) include a decrease in hean rate and blood pressure at rest as well as a decrease in hean rate and blood pressure during sub maximal work. Stroke volume and cardiac output are increased throughout exercise. 1 In addition, aerobic exercise has a strikingly beneficial effect on cholesterol levels. EFFECfS ON CORONARY ARfERY

DISFASE-Several epidemiologic studies have shown that aerobic exercise has a beneficial effect on incidence of and monality &om coronary anery disease. One of the first of these studies5 involved 6,3 51 longshoremen who were 35 to 74 years of age upon entry to the study. Subjects were followed for 22 years or until they reached age 75, unless they died before completion of the study. The age-adjusted coronary continued 103

The beneficial effect of aerobic exercise on incidence of and mortality from coronary artery disease may be due to its effect on cholesterol levels.

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Table 1. Exercise prescription for healthy adults* Frequency

3 to 5 days/wk Intensity

60% to 90% of maximum heart rate Duration

15 to 60 min (continuous) Type of activity

Running, jogging, walking, bicycling, swimming, or other endurance sports "Recommended by the American College of Sports Medicine.

Table 2. Beneficial physiologic responses to aerobic exercise

Decreased resting heart rate and blood pressure Decreased heart rate and blood pressure during submaximal work Increased stroke volume and cardiac output throughout exercise Faster recovery to baseline heart rate and blood pressure Increased maximum oxygen uptake

death rate for those whose activity level was classified as high was 26.9 deaths per 10,000 work-years, whereas the rate for those with a low activity level was 49 deaths per 10,000 work-years. A subsequent studY' examined 16,936 Harvard alwnni aged 35 to 74 years and found that risk of first heart attack was inversely related to

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energy expenditure. Men who expended fewer than 2,000 kcal of energy per week were at 64% higher risk of a first heart attack than classmates who expended more energy. Nwnber of stairs climbed, nwnber of blocks walked, amount of time spent playing strenuous sports, and a composite physical activity index were all used to calculate energy expenditure. The study found that former varsity athletes retained a lower risk only if they maintained a high level of physical activity as alwnni. A British study of 17,944 middleaged male office workers in the civil service- found that men who on an initial survey claimed to engage in vigorous sports had an incidence of coronary artery disease over the next 8Y2 years that was somewhat less than half that of their colleagues who had responded that they got no vigorous exerCise. In a follow-up 8 to the Harvard alwnni study, death rates were found to be one quarter to one third lower among alwnni expending 2,000 or more kcal per week during exercise than among less active men. By the age of 80, those who had gotten adequate exercise between the ages of 35 and 79 had gained 1 to more than 2 years of added life compared with those who had been sedentary. EFFECTS ON BLOOD UPID LEVELS-The changes in blood lipid

levels brought about by regular aerobic exercise may be the best explanation for the decreased incidence of coronary artery disease reported in

the previously described epidemiologic studies. In most studies of endurance or aerobic training, 9 levels of triglycerides and low-density lipoprotein (LDL) cholesterol have been found to decrease and levels of high-density lipoprotein (HDL) cholesterol to increase. The HDL cholesterol level has particular significance when considered in light of the Framingham Heart Study, 10 which found evidence of a strong negative association between HD L cholesterol levels and subsequent incidence of coronary artery disease in both men and women over age 50. This finding was confirmed by the Helsinki Heart Study, 11 which showed a 34% reduction in the incidence of coronary artery disease associated with a marked increase in HDL cholesterol levels and a persistent reduction in levels of total and LD L cholesterol. Several studies have quantitated the amount of exercise needed to significantly increase HDL cholesterol levels. One study12 showed that HDL cholesterol levels generally did not begin to rise until a threshold exercise level of 10 miles (16 krn) run per week was maintained for at least 9 months. In another study, 13 HDL cholesterol levels were compared in marathon runners (who averaged 40 miles [64 krn] per week), joggers (who averaged 11 miles [17.6 krn] per week), and inactive men. The HDL levels averaged 65 mg!dL in the marathoners, 58 mg!dL in the joggers, and 43 mgldL in

AEROBIC EXERCISE • VOL 90/NO 1/JULY 1991/POSTGRADUATE MEDICINE

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A modest program of walking or running 3 miles three times a week will burn 46,800 calories in a year.

the inactive men. Some studies have indicated that when participants are oveiWeight, aerobic activity has a doubly beneficial effect on HDL cholesterol levels, because any weight loss that results also tends to elevate HDL levels. 14

David J. Mersy, MD Dr Mersy is chair of the department of family medicine and director of the family medicine residency program, St PaulRamsey Medical Center/Ramsey Clinic, St Paul, Minnesota. He has special interests in aerobic exercise, graduate medical education, and chemical dependency.

EFFECI'S ON BLOOD PRESSURE-

Aerobic exercise has a beneficial effect on hypertension, another significant risk factor for cardiovascular disease. In one study, 1' exercise three times per week reduced resting blood pressure by 10/7 mm Hg, and exercise seven times per week reduced it by 12/7 mm Hg. Such study results have led many authorities to recommend that nonpharmacologic methods such as aerobic exercise be given a substantial trial in the treatment of mild hypertension.

Weight control Each mile walked or run burns about 100 calories. Some patients become discouraged at the thought of having to walk or run 35 miles to burn off 1 lb of fat. However, a modest program of walking or running 3 miles three times a week will burn 46,800 calories in a year, resulting in a potential weight loss of more than 13lb. There is evidence 16 that reduction of body fat is more easily achieved and maintained when exercise is part of a weight-loss program. One of the problems of treating obesity with very-low-calorie diets is that the resting metabolic rate decreases when the number of calories consumed di-

minishes greatly. Several studies have shown that this fall in resting metabolic rate is reversed by daily exercise. 1Risk of coronary artery disease increases with level of obesity, as demonstrated by a follow-up of participants in the Framingham study. 18 Exercise-induced weight loss may be responsible for some of the cardiovascular benefits of aerobic exercise. As noted already, weight loss through moderate dieting or exercise is partly responsible for the elevated HDL cholesterol levels seen in exercisers.1'' There is evidence that fat distribution has a significant effect on mortality &om coronary artery disease. A significant positive association has been found between malepattern obesity (in which fat is stored above the waist, in the nape of the

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neck, in the shoulders, and in the abdomen) and the incidence of myocardial infarction, angina pectoris, stroke, and death. 20 Aerobic exercise has been shown to be particularly effective in reducing the dangerous abdominal fat associated with this male-pattern obesity. 21

Psychological benefits Most people begin a program of regular aerobic exercise to cut down their risk of coronary artery disease or to help lose weight. But many of these same people continue with an exercise program because of its positive mental benefits: reduction in anxiety and depression, modulation of stress levels, and even personality changes characterized by a more positive outlook on life. One study of healthy, middleaged adults22 showed that subjects continued 105

Exercise can alleviate

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anxiety and depression, perhaps by increasing plasma levels of endorphins.

who exercised exhibited less anxiety, tension, depression, and fatigue, and more vigor, than subjects in a control group. Running has been found to be as effective in treating moderate depression as two kinds of psychotherapy. 23 In a study of depressed women/ 4 subjects in an exercise group had significantly greater decreases in depression than those in the placebo group or the no-treatment group. In a study in which patients in a psychiatric hospital unit exercised regularly, 2' significant decreases in depression were found, along with trends toward a decrease in anxiety and an increase in sense of accomplishment. One way in which exercise may help to alleviate anxiety and depression is by increasing plasma levels of endogenous opioid peptides (endorphins). Some studitS6 '27 have demonstrated that exercise increases plasma levels of endorphins and that cardiovascular training augments this effect. Aerobic exercise is also markedly beneficial in reducing stress, thereby contributing to a healthier life. A meta-analysis of 34 studitS8 showed that aerobically fit subjects had a reduced psychosocial stress response compared with either control group or baseline values. The exact mechanisms of this stress reduction have not been elucidated, but it may be that aerobic exercise causes a decrease in sympathetically mediated cardiovascular responses to psychosocial stress.

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Other benefits In part because of its psychological benefits, regular aerobic exercise is a valuable adjunct to the physician's advice to stop smoking. This beneficial effect probably results from a combination of the following factors: improved self-image, relief of stress and depression, the discarding of a negative activity in favor of an overall healthier approach to life, and the incompatibility of smoking with a desire to achieve maximum fimess. Many researchers believe that exercise can help prevent osteoporosis.29 The 1984 National Institutes of Health Consensus Development Panel10 recommended a program of "modest weight-bearing exercise" for possible prevention of osteoporosis. Other investigators have been more reserved in their judgrnent. 31 Until more evidence is in, it probably would be unwise to recommend aerobic exercise solely to prevent osteoporosis. However, knowing that such prevention is a potential benefit can be an added inducement to undertake an exercise program, particularly for middle-aged women. For many years, physical exercise has been considered beneficial for patients with diabetes mellitus. 12 These patients are particularly in need of the protection against coronary artery disease that exercise provides. In addition, exercise increases glucose utilization and decreases insulin requirements. Of course, this means that caloric intake during exercise or adjustment of the insulin

regimen to provide less insulin effect at the time of exercise may be necessary. Patients must also guard against delayed hypoglycemia, which may occur from 12 to 24 hours after vigorous exerciSe. Additional possible benefits of aerobic exercise include improvement in some of the metabolic abnormalities in hemodialysis patients/3 higher rates of abstinence in alcoholics,34 and greater motor proficiency in the mentally retarded. 35

Exercise during pregnancy Pregnant women receive the same benefits from exercise as the rest of the population. The American College of Obstetricians and Gynecologis~ recommends that pregnant women exercise for periods of no longer than 15 minutes, not allowing heart rate to exceed 140 beats per minute and not allowing core temperature to exceed 38°C (I00.4°F). These guidelines, developed in 1985 and designed to be safe for 99.9% of the pregnant population, have been thought by some to be too conservative. 37 On the basis of a review of the literature, Jarski and Trippetf8 have developed recommendations that are somewhat more liberal (table 3). Exercise and aging As the geriatric population of the United States continues to grow, increasing numbers of older people are interested in preserving their vitality into old age. Aerobic exercise can

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Maximum oxygen consumption declines with age at a rate of about 1% per year, but a program of physical activity markedly alters this decline.

certainly be of benefit in this respect. Aging has significant physiologic consequences. Maximum oxygen consumption declines with age at a rate of about 1% per year, but a program of physical activity markedly alters this decline. 39 Also, lean body mass decreases and fat mass increases with age. Numerous studies have shown that an active exercise program can reverse some of these changes in body composition in older people.40 Elderly men and women are capable of demonstrating a training effect in response to endurance training regardless of their previous panems of physical activity and current levels offimess.4' Other favorable physiologic changes that have been noted in geriatric patients who exercise indude decreased cholesterol levels, decreased diastolic blood pressure levels, and a trend toward increased bone mineral content.42

Table 3. Recommendations for and contraindications to exercise during pregnancy Recommendations

Comprehensive prenatal evaluation Patient education on exercise, self-monitoring of heart rate 30 min of aerobic exercise 3 times per week Body temperature never > 40°C Heart rate < 70% of maximum Heart and respiratory rates should return to resting rates within 15 min after exercising Frequent rest periods Ideal activities: swimming, biking, aerobic walking Alternative activities: stretching exercises and normal walking for those unable to exercise aerobically Activities to avoid: sitting in hot tubs or saunas; strenuous activity in hot or humid environments; activities at high altitudes that induce shortness of breath; snorkeling or scuba diving Contra indications

Anemia Thyrotoxicosis Hypertension, heart disease Mild or severe preeclampsia Premature labor, cervical bleeding Multiple pregnancy History of complicated pregnancy Adapted from Jarski and Trippett."

Potential problems Aerobic exercise programs can result in injuries, particularly if caution is not used. For persons starting a running or walking program, proper shoes are of utmost importance and can help prevent shin splints, chondromalacia, muscle soreness, hamstring strain, and low back pain, which are the injuries most likely to occur in joggers.43 Injuries can be minimized by using the proper equipment and by limiting increases in the amount of time spent performing the aerobic activity

to 10% per week Sudden death in runners has been a concern of the public, especially since popular running author Jim Fixx died while running several years ago. Most of these infrequent deaths have resulted from underlying coronary artery disease. 44 The most conservative approach to prevention of sudden death is to do treadmill stress testing for all patients over age 35 who are planning to start an aerobic exercise program.' A more practical approach is to do ex-

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ercise stress testing only for persons who have one or more risk factors for coronary artery disease or who are about to embark on a quite vigorous program. Advising exercisers to pay anention to symptoms of heart disease and to stop exercising if they have chest pain, shortness of breath, or other cardiac symptoms may be more important than performing stress tests. Athletic amenorrhea may occur in young women who exercise vigorously. This problem is seen most ofcontinued on page 110 107

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Briel Summary, Contnlndlcatlons, Patients who have had allergiC react1oos to NAPROSYN, ANAPROX or ANAPROX OS or in whom aS!)irin or other NSAIDs induce the syn· drome of asthma, rhinitiS, and nasal polyps. Because anaphylactic react1oos usu· ally occur in patients with a hiStory of such reactioos, questioo patients for asthma, nasal polyps. urticar~. and hypotensioo associated with NSAIDs before starting therapy. If such symptoms occur, discontinue the drug. wamtnp, Serious Gl toxicity such as bleeding, ulceratioo, and perforatioo, can occur at any time, wrth or wrthout warning symptoms. in patients treated chron1· cally with NSAIDs. Rernam alert for ulceratioo and blee

Health benefits of aerobic exercise.

Regular aerobic exercise has significant cardiovascular benefits, including a reduction in incidence of and mortality from coronary artery disease--pr...
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